I started off playing on normal/normal difficulties because I always get smashed if I play anything higher, especially on the campaign map. I also started off with the imperialist Mori clan (they're not actually called Mori but in their description it says they are the Mori but got moved a bit further west) because they have bonuses to industrialisation.

Also in the battles you have to be careful at the start because the enemy samurai units will rip your line infantry/levy muskets to pieces if they got close - which they will, because they fire slow until you get kneel fire. The way I fought was to have a line of muskets and directly behind them a line of spear levies/yari samurai. Let the muskets fire one or two rounds as they approach then charge them with your spear levies.